One-piece plastic clamps used to pinch off plastic tubing, such as polyvinyl chloride (PVC) tubing are well known. Examples are found in U.S. Pat. Nos. 6,196,519, 6,089,527, D431,650, and 616,1812. Known clamps are formed from a single strip of plastic in which the respective ends are curved towards each other to engage together in a snap-fit. The curved portion may generate a restoring force that is opposed by interfering relationship of catches at the ends of the strip, thereby providing the snap-fit engagement. Pinch projections on the inner side of the strip squeeze the tubing shut when the ends of the strip are engaged. The tubing can be opened by releasing and permitting the separation of the engaged ends.
The strip portion of known clamps may have two opening in the middle of the strip. These openings may be arranged so that the tube can pass between the openings and through the middle of the strip so that it is positioned between the pinch projections.
The engagement of known clamps can be performed improperly such that cross-clamping occurs. In this situation, it is possible for the pinch clamp to spontaneously disengage or to pinch the tube incompletely or with inadequate force. Also, clamps are used in large number in disposable tubing sets and it is desirable for them to have high performance but low cost. For example, pinch clamps have been used in the dialysis blood tubing sets for many years. Thus, there is a continuing need for improvements in the design of clamps to provide reliability, ease of use, and low cost.